Influenza has a long standing history of pandemics, epidemics, resurgences and outbreaks. Vaccines have been the most effective defense against influenza. However, the effort to design and manufacture vaccines that induce strain-specific immunity year-over-year has been difficult and influenza continues to cause significant health problems across the globe. Indeed, currently marketed influenza vaccines must be updated annually based on predicted strains that will be present in human populations in the impending season.
Current influenza vaccines are based on inducing immunity to the hemagglutinin antigen present on the surface of influenza viruses. Hemagglutinin (HA) is a glycoprotein responsible for the binding of the influenza virus to cells with sialic acid-containing on surface structures on their membranes, and is highly variable across influenza virus strains. Among the current strategies for vaccination against influenza, the development of a universal vaccine holds the promise to increase the breadth of current strain-specific vaccines by focusing on relatively conserved regions of HA.